Conveniently, the Tea Party Patriots are organized as a social welfare organization, [501(c)4 of the tax code], therefore not regulated by federal finance campaign laws and not required to disclose funding sources.

"As long as the Tea Party Patriots do not mention candidates' names in their material or explicitly advocate for or against a specific candidates' election, they don't have to meet federal requirements to disclose their donors.[...] There certainly seems to be an increase in the use of 501(c)4s to launder political donations. Big donors find them attractive because they can give money without getting their names in public." -- Paul Ryan, an expert at the Campaign Legal Center, a non-partisan watchdog group that monitors election law.

However, despite the anonymity of the donor, thanks to Jane Mayer's article in The New Yorker, Covert Operations, it's fairly safe to assume that the incredibly rich Koch brothers, of Koch Industries, an oil refiner and the nation’s second largest private company with about $100 billion in annual revenue, and who are tied at #24 on Forbes top billionaire's list are behind most large donations.

Many of the groups on the right receive funding from a network of influential conservative foundations, including those connected to the Koch brothers of Wichita, Kan., who run the largest private energy firm in the United States. Records show that the Koch-connected Claude R. Lambe Charitable Foundation, for example, has given $3.1 million to Americans for Prosperity, a group that has taken a leading role in organizing "tea party protests" and other anti-reform efforts.